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SonoTutorial: Appendicitis assessment by ultrasound #FOAMed #FOAMus

In a recent article in Insights into Imaging, there is a great pictorial and descriptive review of the how-to of appendicitis assessment by ultrasound. The authors are radiologists from the UK and they provide an excellent description of its assessment. As they state, if appendicitis is not evaluated in patients with right lower quadrant pain or any of the other signs of appendicitis (either by the Alvarado Score or other decision rule… or even just your clinical judgement) complications can occur: “Potential complications include perforation, peritonitis, abscess formation and death. Because of atypical presentations and the risk of potential complications, imaging is often requested. In children, this imaging technique is usually US.” For SonoSpot cases for appendix US, go here. For SonoSpot studies’ reviews in appendicits, go here. A great lecture through AEUS on appendicitis and ultrasound, go here.

Their specific teaching points:

• A step-wise technique improves the chances of visualisation of the appendix.

• There are often several causes for the non-visualisation of the appendix in children.

• A pathological appendix has characteristic US signs, with several secondary features also identified.

• There are multiple common differentials to consider in the paediatric patient.

“Setting the scene: contact with the patient and parents

When meeting the paediatric patient for the first time, the patient should be asked where the point of maximum tenderness is located. The examination is explained to the patient. The patient is usually accompanied by a parent or guardian. In optimal conditions, the patient is fasted and has a full bladder to help in the exclusion of any ovarian or other pelvic pathology.

Graded compression US

The scan is continued with a planar higher frequency probe, which allows higher resolution of more superficial structures. The frequency used depends on the size and age of the child (between 5 and 12 MHz).

Step 1:

Displacing small bowel loops out of the way

Normal bowel loops are displaced by gentle compression of the anterior abdominal wall using the US probe. These loops should be easily compressed and displaced away. The displacement of the bowel structures should allow the visualisation of the iliac vessels in the right iliac fossa as well as the psoas muscle. Two-plane scanning is performed (longitudinal and transverse).

Step 2:

Visualisation of the ascending colon and caecum

The ascending colon is visualised as a non-peristalsing structure containing gas and fluid in the right side of the abdomen. The probe is then moved inferiorly toward the caecum, using repeated compression and release to express gas and fluid from the bowel (Fig. 1a, b). The right psoas muscle should also be visualised (Fig. 2). The adjacent terminal ileum should be identified as a compressible structure that is undergoing peristalsis.

Fig. 1

Longitudinal (a) and transverse (b) views using high frequency linear-array probe showing the caecum (small white arrows in b) and ascending colon in a 15-year-old girl

Fig. 2

Longitudinal image showing the caecum and ascending colon, as well as the adjacent psoas muscle posteriorly (small white arrows) in a 15-year-old girl

Step 3:

Identification of the appendix

Once the caecum has been seen, the appendix should be visualised arising from it, separate to the terminal ileum (Fig. 3). The appendix should be followed along its whole length. A normal appendix should measure 6 mm or less in diameter from outside wall to outside wall. It should have a thin wall (less than 3 mm), be empty or gas/faecal-filled and compressible, and there should be no evidence of hypervascularisation [23–26].

Fig. 3

A normal appendix is seen draped over the iliac vessels in a 10-year-old girl. This is thin-walled, measuring less than 6 mm in diameter (A width of 3 mm). The caecum can be seen in continuity with the appendix superior to it

Step 4:

Assessment for features of acute appendicitis

An abnormal appendix can have any of the following characteristics which should be actively considered:

Compressibility: in acute appendicitis, the appendix is non-compressible [24]. One caveat here is perforation when the appendix can become compressible.

Maximum diameter: a maximum diameter of greater than 6 mm is considered abnormal (Figs. 4 and 5) [5, 24, 25].

Wall thickness: a single wall thickness of 3 mm or more is considered abnormal (Fig. 6) [24, 27].

Target sign appearance: this is caused by a fluid-filled centre (hypoechoic centre), surrounded by a hyperechoic ring (mucosa/submucosa) which is surrounded by a hypoechic muscularis layer giving a target sign on axial imaging (Fig. 7a, b) [15, 28].

The presence of an appendicolith (this will appear as an echogenic focus with posterior acoustic shadowing) (Fig. 8a, b) [15, 28].

Vascularity: peripheral appendiceal wall hyperaemia is seen in the early stages of acute appendicitis (Fig. 9a, b); this may not be seen with progression to necrosis [15, 29].

Focal apical caecal pole thickening or thickening of the adjacent small bowel can be seen as a secondary response [6, 30].

Fig. 10

Small pocket of free fluid in the region of the appendix (white arrow) in a 10-year-old girl with confirmed appendicitis

Fig. 11

Omental fat with increased echogenicity with a mass-like appearance (small white arrows) in a 12-year-old boy with confirmed appendicitis

Fig. 12

Multiple lymph nodes (arrows) in the mesentery of the periappendiceal region in an 8-year-old girl with confirmed appendicitis

Fig. 13

Increased echogenic free fluid in the right iliac fossa (indicating pus) with adjacent thickening of the peritoneum in a 2-year-old girl with confirmed appendicitis

Fig. 14

Loops of dilated, fluid-filled small bowel in a 2-year-old girl with confirmed appendicitis. Echogenic free fluid is seen adjacent to the bowel indicating pus (white arrow)

It is not uncommon that the appendix cannot be identified. There are varying rates quoted in the literature for the appendix being seen, between 24.4 % and 69.3 % [6, 13, 23]. In this situation, it is important to actively assess for the secondary features often seen which may help direct further management. Repeating the examination after a few hours has been shown to significantly increase the sensitivity of US [31].

Read on more to hear about the complications of appendicitis, the causes of inadequate visualization, and other etiologies as seen on ultrasound for right lower quadrant pain. Trust me, its worth the viewing.